Transposon-activated POU5F1B promotes colorectal cancer growth and metastasis

The treatment of colorectal cancer (CRC) is an unmet medical need in absence of early diagnosis. Here, upon characterizing cancer-specific transposable element-driven transpochimeric gene transcripts (TcGTs) produced by this tumor in the SYSCOL cohort, we find that expression of the hominid-restricted retrogene POU5F1B through aberrant activation of a primate-specific endogenous retroviral promoter is a strong negative prognostic biomarker. Correlating this observation, we demonstrate that POU5F1B fosters the proliferation and metastatic potential of CRC cells. We further determine that POU5F1B, in spite of its phylogenetic relationship with the POU5F1/OCT4 transcription factor, is a membrane-enriched protein that associates with protein kinases and known targets or interactors as well as with cytoskeleton-related molecules, and induces intracellular signaling events and the release of trans-acting factors involved in cell growth and cell adhesion. As POU5F1B is an apparently non-essential gene only lowly expressed in normal tissues, and as POU5F1B-containing TcGTs are detected in other tumors besides CRC, our data provide interesting leads for the development of cancer therapies.


March 2021
For manuscripts utilizing custom algorithms or software that are central to the research but not yet described in published literature, software must be made available to editors and reviewers. We strongly encourage code deposition in a community repository (e.g. GitHub). See the Nature Portfolio guidelines for submitting code & software for further information.

Data
Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A description of any restrictions on data availability -For clinical datasets or third party data, please ensure that the statement adheres to our policy Field-specific reporting Please select the one below that is the best fit for your research. If you are not sure, read the appropriate sections before making your selection. Analyses of publicly available datasets used all available samples and multiple independent datasets were used to corroborate the reproducibility of the findings. Sample size in the animal experiments was determined in accordance with power analyses done based on previous experiments, where: a) to achieve a pval <0.05 it was necessary to have, at least, n=7 animals per group; b) a certain number of animals may have to be excluded from the experiment due to the complexity of the intervention. The graft rate may vary between 80-100% between animal models; c) it is necessary for the results to be reproducible. The number of mice depending on the type of tumor implantation varied as follows: -For the subcutaneous implantation of cell lines we used n = 7-8 animals per condition.
-For intra-splenic injection of cell lines we used n = 7-9 animals per condition.
-For orthotopic implantation of tumor fragments we used n = 10 animals per condition.

Reporting for specific materials, systems and methods
We require information from authors about some types of materials, experimental systems and methods used in many studies. Here, indicate whether each material, system or method listed is relevant to your study. If you are not sure if a list item applies to your research, read the appropriate section before selecting a response. No data were excluded from the analysis, except for Supplementary Figure 2d, in which one SW620 GFP animal died post surgery.
All in vitro experiments were reproduced a minimum of 2 to 3 independent times with 3 to 12 technical replicates each, using the same experimental approach. Number of replicates and sample sizes are provided for each of the experiments in figure legends. Findings and conclusions in the manuscript represent those that were consistent across independent experiments. Attempts at replication were successful. In line with the 3R principles (Reduce, Refine, Replace), in vivo experiments were performed once each, albeit ensuring that sample size was appropriate to reach statistical significance.
Animal randomization was achieved by having mice injected with different conditions within the same cage. Randomization was not relevant for other experiments described in this study.
All in vitro and in vivo experiments were conducted by experimenters blinded to the experimental conditions. When possible, control and test condition were seeded into the same plate to avoid possible technical biases.
The anti-POU5F1B antibody was extensively validated in the lab upon arrival. OCT4 and POU5F1B positive and negative cells were used for immunohistochemistry validation.
The other antibodies were used under the manufacturer specifications, being the vast majority of them validated previously in our lab: > Anti-HA-Biotin, High Affinity (3F10) is a monoclonal antibody for the highly sensitive detection of HA-tagged recombinant proteins, Fab fragments, conjugated to biotin. The Anti-HA-Biotin, High Affinity antibody (clone 3F10) recognizes the same epitope as clone 12CA5. It is a monoclonal antibody whose high affinity and low working concentrations result in less cross-reactivity than with other antibodies to the HA-epitope. Anti-HA-Biotin, High Affinity (3F10) is a biotin conjugate of this clone which is specifically useful in western blotting, ELISA applications and assays using the universal biotin-streptavidin platform, by allowing specific and highly sensitive detection of HA-tagged proteins.